Spiro and dispiro quaternary ammonium compositions



United States Patent 3,055,171 SPIRO AND DISPIRQ QUATERNARY AMMONIUM CGMPOSITIONS Howard W. Best and Richard C. Doss, Bartlesviile, Okla, assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Sept. 9, 1960, Ser. No. 55,096

19 Claims. (Cl. 60-35.4)

This invention relates to monopropellant compositions suitable for use in rocket motors, ram-jets, pulse-jets, and the like. In a further aspect, this invention relates to a method of operating such motors.

Rocket motors are operated by burning a mixture of fuel and oxidant in a combustion chamber thereof and causing the resulting gases to be expelled through a nozzle at high velocity. Liquid propellants are usually preferred over solid propellants where it is necessary to vary thrust during flight. Liquid propellants can be classified as bipropellants and monopropellants, and the latter can be either a single compound or mixtures of compounds. Monopropellant systems are advantageous in that they require only one tank, one pump, one nozzle, one fuel line, one set of controls, etc. Furthermore, no mixing or proportioning system is required.

The principal elements of a rocket motor utilizing a liquid fuel comprise a combustion chamber, exhaust nozzle, an injection system, and propellant control valves. The propellant gases are produced in the combustion chamber at pressures governed by the chemical characteristics of the propellant, its rate of consumption, and the cross-sectional area of the nozzle throat. The gases are ejected into the atmosphere through the nozzle with supersonic velocity. The function of the nozzle is to convert the pressure of the propellant gases into kinetic energy. The reaction of the discharge of the propellant gases constitute the thrust developed by the rocket motor.

An object of this invention is to provide new monopropellant compositions. A further object of this invention is to provide a method for operating rocket motors. Other aspects, objects and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

In accordance with the invention there are provided new monopropellant compositions which are suitable for use according to the method of the invention in rocket motors and the like. Broadly speaking, the invention comprises a mixture of a spiro quaternary ammonium compound and/ or a dispiro quaternary ammonium compound and a suitable oxidant as a monopropellant composition, and the use of said composition as a propellant in a rocket motor or the like.

Thus according to the invention there is provided a monopropellant composition comprising a mixture of (1) an oxidant selected from the group consisting of nitric acid containing at least about 70 weight percent HNO and mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 weight percent HClO and not more than about 30 Weight percent water, and (2) at least one compound selected from the group consisting of spiro quaternary ammonium compounds characterized by Formula I below and dispiro quaternary ammonium compounds characterized by Formula ll be low, and mixtures thereof,

wherein: each R is selected from the group consisting of a hydrogen atom and alkyl radicals containing from 1 to 3 carbon atoms, and wherein not more than one R in each ring is an alkyl group; x and y are each integers of from 4 to 8; X is an anion selected from the group consisting of nitrate, perchlorate, monohydrogen phosphate, dihydro gen phosphate, hydrogen sulfate, sulfate, hydroxyl, orthoborate, dihydrogen borate, and tetraborate anions; a and b are each integers of from 1 to 4, and the product of a multiplied by the number of quaternary nitrogen atoms is equal to the product of b multiplied by the valence of said anion X; and wherein the ratio of said quaternary ammonium compound to said oxidant is within the range of 0.75 to 1.25 times that of the stoichiometric amount.

It is to be noted that the compounds used in the practice of the invention are spiro quaternary ammonium compounds and dispiro quaternary ammonium compound as distinguished from acid salts of amines. The two classes of compounds are distinctly diiferent chemically. As used herein and in the claims the words quaternary ammonium compound refers to a compound containing at least one nuclear nitrogen atom having its five so-called valence bonds attached to atoms (or radicals) other than a hydrogen atom. For example, such as four nitrogen to carbon bonds and one nitrogen to nitrate (or other anionic radical) bond. In other words, the available valence bonds of said nuclear nitrogen atom are satisfied by other than a hydrogen radical. For example, consider the two compounds (1) trimethylamine nitrate and (2) tetramethyl ammonium nitrate which have the formulas (CH NHNO and (CH NNO respectively. It will be noted that in the acid salt trimethylamine nitrate one of the valence bonds of the nuclear nitrogen atom is satisfied by a hydrogen atom whereas in the quaternary ammonium compound tetramethyl ammonium nitrate all five valence bonds are satisfied by radicals other than hydrogen.

The two classes of compounds can also be distinguished by their reaction with strong bases. For example, when an acid salt such as trimethylarnine nitrate is reacted with sodium hydroxide the amine is liberated along with the formation of sodium nitrate and water; whereas a quaternary ammonium compound such as tetramethyl am monium nitrate has no hydrogen available for the formation of water and there is obtained the tetramethyl ammonium hydroxide, (CH NOH and sodium nitrate, and no free amine is liberated.

The quaternary ammonium compounds used in the practice of the invention are further distinguished from ordinary quaternary ammonium compounds, such as those just discussed, in that the compounds of the invention are either spiro quaternary ammonium compounds or dispiro quaternary ammonium compounds.

Spiro compounds are defined as compounds containing a spiro atom, i.e., an atom forming the only common member of two rings. Compounds containing two spiro atoms are called dispiro compounds. The structural formulas of spiro compounds can be said to have the general configuration of a figure 8 with the spiro atom at the point of tangency of the two rings. For example, the compound N,N-pentamethylenepiperidinium nitrate can be said to have the structural formula and the compound N,N,N,N-diethylene dipiperidinium dinitrate can be said to have the structural formula o In N,N-tetramethylenepyrrolidinium nitrate N,N-tetramethylenepyrrolidinium perchlorate N,N-( l-methyltetramethylene -2-methy1pyrrolidi-niurn nitrate N,N-pentamethylenepyrrolidinium nitrate N,N-pentamethylenepyrrolidinium dihydrogen phosphate N,N- 3-ethylpentamethylene) -2-methylpyrrolidinium nitrate N,N-hexamethylenepyrrolidinium nitrate N,N-hexamethylenepyrrolidinium hydrogen sulfate N,N-hexamethylene-3-propylpyrrolidinium nitrate N,N-heptamethylenepyrrolidinium nitrate N,N-heptamethylenepyrrolidinium hydroxide N,N- B-methylheptamethylene) -2-ethylpyrrolidinium nitrate N,N- S-methylheptamethylene) -2-ethylpyrrolidinium dihydrogen borate N,N-octamethylenepyrrolidinium nitrate N,N-2-methyloctamethylenepyrrolidinium nitrate Bis(N,N-Z-methyloctamethylenepyrrolidinium) sulfate N,N-pentamethylenepiperidinium nitrate N,N-( l-methylpentamethylene) -2-methylpiperidinium nitrate Bis(N,N-(1-methylpentamethylene) 2 methylpiperidinium) tetraborate N,N-hexamethylenepiperidinium nitrate N,N- 3 -propylihexamethylene) piperidinium nitrate Tris(N,N-(3-propylhexamethylene)piperidinium) orthoborate N,N-heptamethylene-Z-methylpiperidinium nitrate N,N-octamethylenepiperidinium nitrate N,N-(Z-methyloctamethylene) piperidinium nitrate N,Nhexamethylene-hexamethyleneimine nitrate Bis(N,N-hexamethylene-hexamethyleneimine) monohydrogen phosphate N,N- 3 -ethylhex amethylene) -hexamethyleneimine nitrate N,N-heptamethylene-hexamethyleneimine nitrate N,N-(2-propylheptamethylene) 3 methylhexamethyleneimine nitrate 4 N,N-octamethylene-hexamethyleneimine nitrate N,N- 4-methyloctamethylene) -hexamethyleneimine nitrate N,N-heptamethylene-heptamethyleneimine nitrate N,N-(Z-methylheptamethylene) 3 methylheptamethyleneimine nitrate N,N-octamethylene-heptamethyleneimine nitrate N,N-octamethylene-2-ethylhep-tamethyleneimine nitrate N,N-octamethylene-octamethyleneimine nitrate N,N,N,N-di(tetramethylene)piperazrinium dinitrate N,N,N,N'-di tetramethylene) -methylpiperazinium dinitrate N,N,N ,N-di (tetramethylene) -methylpip er azinium diperchlorate N,N-tetramethylene-N',N'-pentamethylenepiperazinium dinitrate N,N-( l-methyltetramethylene) -N',N'-pentamethylcnep-iperazinium dinitrate N,N-( l-methyltetramethylene) -N',N'-p entamethylenepiperazinium diperchlorate N,Ntetramethylene-N,N-hexamethylenepiperazinium dinitrate N,N-tetramethylene-N,N-(Z-ethylhexamethylene) piperazinium dinitrate N,N-tetramethyleneN,N-(2-ethylhexamethylene) piperazinium monohydrogen phosphate N,N-tetramethylene-N,N'-heptamethylenepiperazinium dinitrate N,N-tetramethylene-N',N-heptamethylenemethylpiperazinium dinitrate N,N-tetramethylene-N,N-octamethylenepiperazinium dinitrate N,N-tetramethylene-N,N'-octamethylenepiperazinium di(dihydro-gen phosphate) N,N-tetramethylene-N',N- 3-methyloctamethylene) piperazinium dinitrate N,N,N,N-di(pentamethylene)piperazinium dinitrate N,N,N',N-di(pentarnethylene)piperazinium di(-l1ydrogen sulfate) N,N-pentamethylene-N',N'-(2-propylpentamethylene) piperaziniurn dinitrate N,N-pentamethyleneN',N-hexamethylenepiperazinium dinitrate N,N-pentamethylene-N',N-hexamethylenepiperazinium sulfate N,N-l-methylpentamethylene-N',N'-hexamethyler1epiperazinium dinitrate N,N-pentamethylene-N',N-heptamethylenepiperaziniurn dinitrate N,N-pentamethylene-N,N'-heptamethylenepiperazinium dihydroxide N,N-pentamethylene-N,N'-(Z-methylheptamethylene) piperazinium dinitrate N,N-pentamethylene-N,N-octamethylenepiperazinium dinitrate Tris N,N-pentamethylene-N',N'-octamethylenepiperazinium) diborate N,N-pentamethylene-N',N- 3-propyloctamethy1ene) piperaninium dinitrate N,N,N',N'-di(hexamethylene)piperazinium dinitrate N,N,N',N'-di(hexarnethylene)piperazinium di(dihydrogen borate) N,N,N,N'-di(hexamethylene) -ethylpiperazinium dinitrate N,N-hexamethylene-N,N'-heptamethylenepiperazinium dinitrate N,N-hexamethylene-N,N'-heptamethylenepiperazinium tetraborate N,N- Z-methylhexamethylene) -N,N'-heptamethylenepiperazinium dinitrate N,N-heXamethylene-N',N'-octamethylenepiperazinium dinitrate N,N-hexamethylene-N,N'-octamethylenepiperazinium tetraborate N,N-hexamethylene-N',N'-( S-methyloctamethylene) piperazinium dinitrate N,N,N',N'-di (heptamethylene) piperazinium dinitrate N,N,N,N'-di (heptamethylene) -3 -methylpiperazinium dinitrate N,N-heptamethylene-N',N-octamethylenepiperazinium dinitrate N,N- 1 -methylheptamethylene -N,N-( l-methyloctamethylene) piperazinium dinitrate N,N,N',N-di octamethylene) piperazinium dinitrate The spiro quaternary ammonium compounds and the dispiro quaternary ammonium compounds described above are oxygen deficient and consequently the monopropellant fuel compositions of the invention require an oxidant. Nitric acid is the presently preferred oxidant for use in the practice of the invention. Since water tends to retard combustion of the acid with the fuel, the nitric acid is preferably substantially free of water. Thus, the presently most preferred oxidant is anhydrous nitric acid. However, other more dilute nitric acids can be used in the practice of the invention. White fuming nitric acids and red fuming nitric acids of varying concentrations are available commercially, and all are useful in the practice of the invention. White fuming nitric acid usually contains about 90 to 99 weight percent HNO from 0 to 2 weight percent N0 and up to about weight percent water. Red fuming nitric acid usually contains about 70 to 90 weight percent HNO from 2 to weight percent N0 and up to about 10 weight percent water. Of course, mixtures of the above described acids can be employed to give an acid having an intermediate composition, and all are useful in the practice of this invention. Thus, it has been found that nitric acids of all types containing at least about 70 Weight percent HNO are useful as an oxidant in the practice of the invention.

In addition, it is within the scope of the invention to use mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 weight percent HCIO as an oxidant in the practice of the invention. Said mixtures preferably do not contain more than about weight percent water.

The monopropellants used in the present invention will be preferably near stoichiometric mixtures of oxidant and a spiro and/or a dispiro quaternary ammonium compound. The ratio of fuel component to oxidant can be in the range of 0.75 to 1.25 times that of the stoichiometric amount. In the practice of the invention said quaternary compounds are commonly used in amounts of about 17 to about 48 weight percent of the mixture of oxidant and quaternary compound. A slightly fuel-rich mixture is usually required to given an optimum rocket motor performance. As used herein stoichiometric ratio is that ratio of fuel to oxidant calculated by assuming complete combustion of the nitrogen, hydrogen, and carbon of the fuel to N H 0, and CO respectively.

The normally preferred procedure for preparing the monopropellants of the invention is to admix the spiro and/or dispiro quaternary ammonium compound, prepared by any suitable method, with nitric acid or other suitable oxidant in the desired ratio at some time prior to use. It is generally preferred to add said quaternary compound to the acid oxidant at temperatures below about 50 C., e.g., 0 to 30 C., with good agitation. The length of storage prior to use will depend upon the storage stability of the particular monopropellant composition being employed as will be shown hereinafter.

The spiro and/or dispiro quaternary ammonium compound-nitric acid monopropellants of the present invention can be conveniently ignited by contacting a stream of the monopropellant with a stream of a hypergol such as pyrrole. Any material which is hypergolic when mixed with nitric acid can be used as said hypergol. Other materials hypergolic with nitric acid such as N,N,N',N- tetramethylpropane-1,3-diamine; N,N,N,N'-tetramethylpropene-l,3-diamine; furfuryl alcohol; ethylenediamine; etc., can also be used to ignite the two-component monopropellant. Such a hypergol is simultaneously injected into the combustion chamber with the two-component monopropellant to ignite the monopropellant. After the two-component monopropellant is ignited, the flow of hypergol is stopped. A temperature-sensitive element, a time mechanism, or other means can be used to terminate the flow of the hypergol. The monopropellant compositions of the present invention can also be ignited by other means such as, for example, by an electric igniter The spiro and dispiro quaternary ammonium compounds used in the practice of the invention can be prepared by any of a number of suitable methods well known to those skilled in the art. The following illustrate methods which can be employed to prepare spiro and dispiro quaternary compounds used in the practice of the invention.

N,N-PENTAMETHYLENEPIPERIDINIUM NITRATE (a) N,N pcmamerhylenepiperia'inium bromide-A mixture of pentamethylene bromide (230 grams, 1.0 mole), sodium hydroxide (40 grams, 1.0 mole) and water (1.0 liter) was stirred and refluxed at C. while piperidine (85 grams, 1.0 mole) was added dropwise during the course of one-half hour. After the mixture had been stirred for an additional one-half hour, a clear solution was obtained. The mixture was cooled to 5 C. (41 F.) and 500 milliliters of cold 40 percent aqueous sodium hydroxide was added. An oily layer formed. This layer was diluted five-fold with acetone whereupon a crystalline product formed. This material was filtered and recrystallized from isopropyl alcohol. The material melted when heated to 310 C. (590 F.).

(b) N,N-pentamethylenepiperidinum nitrate-Method A.-N,N pentamethylenepiperidinium bromide (6.2 grams, 0.026 mole) prepared as described above was dissolved in water (30 milliliters) and to this solution was added with stirring a solution which contained silver nitrate (4.5 grams. 0.026 mole) dissolved in water (20 milliliters). After the addition, the mixture was filtered and the filtrate was evaporated under vacuum to near dryness on a steam bath. The residue was recrystallized from isopropyl alcohol. A white crystalline product was obtained which melted with decomposition between 180- C. (346374 F.).

(c) N,N-pentamethylenepiperidinium nitrate-Method B.-N,N-pentamethylenepiperidinium bromide (124.7 grams, 0.53 mole) prepared as described above was added portionwise at 50 C. to a solution which contained nitric acid (200 grams, 3.19 moles) and water (200 milliliters). The addition was made While a stream of air was bubbled through the stirred acid solution. Bromine fumes were constantly being evolved during the addition. After the addition was complete, heating and stirring was continued while air was passed through until the solution was clear. The mixture was cooled and an equal volume of acetone plus a two-fold addition of ether was made whereupon a crystalline material formed. This product was filtered and recrystallized from isopropyl alcohol. A near quantitative yield of the nitrate salt was obtained which melted when heated between 178-188" C. (352370 F.).

N,N,N,N-DIETHYLENEDIPIPERIDINIUM DINITRATE (a) N,N,N,N-diethylenedipiperiainium dibr0mide.- A mixture of piperidine (44.5 grams, 0.5 mole), sodium hydroxide (20.0 grams, 0.5 mole) and Water (60 milliliters) was stirred and ethylene bromide (94.0 grams, 0.5 mole) was added dropwise at such a rate that the mixture refluxed (95 C., 203 F). After the addition, the mixture was stirred and refluxed for 6 hours. The mixture was then cooled and the precipitated product was filtered and washed with methyl alcohol. The crystalline material was purified by dissolving it in water, adding Norite (an activated charcoal), boiling and filtering. To the filtrate was added twice its volume of isopropyl alcohol whereupon a very fine white material separated. The

7 product was filtered, washed with diethyl ether and vacuurn dried. It melted when heated to 345 C. (653 F.). (b) N,N',N,N' Diethylenedipiperidinium dinitrate Method A.N,N',N,N' diethylenedipiperidinium dibro- 8 grams, 0.365 mole) prepared as describde above was added portionwise at 50 C. (122 F.) to a solution which contained nitric acid (200 grams, 3.19 moles) and water (200 milliliters). The addition was made while a stream mide (17.2 grams, 0.0447 mole) prepared as de ibed of air was bubbled through the stirred acid solution. After above was dissolved in water (125 milliliters) and to this the add-10011 Was p Stlfrlflg solution was added, with stirring and cooling, a solution Was cfmtlllufid and 31f Was P through the Solution which contained silver nitrate (15.2 grams, 0.089 mole) i It Was free 0f h bromine Whlch Was P j y dissolved in water (40 milliliters). After the addition, s evolved- The Immune w cooled and d l w the mixture was filtered and the filtrate evaporated t near a three-fold volume of acetone. The crystalllne material dryness under vacuum on a tea bath, Th e id was which formed was filtered and recrystalllzed from methdissolved in 90 percent m tha ol, No it dd d, d th anol. A near quantitatlve yleld of the dmitrate salt which I O m1xture filtered. To the filtrate was added diethyl ether decomposed When heated 191130? was whereupon a crystalline material separated. This rnar Obtalnedterial was filtered, washed with diethyl ether and vacuum EXAMPLE I dried. It did not melt when heated to 300 C. (572 F.). Spiro and dispiro quaternary ammonium compounds (0) N,N',N,N' diethylenedipiperidinium dinitrateprepared by one of the above described procedures were Method B.N,N',N,N' diethylenedipiperidinium dibroadmixed with anhydrous nitric acid at room temperature mide (138 grams, 0.36 mole) prepared as described above in stoichiometric proportions. Properties of the mixtures was added portionwise at 50 C. (122 F.) to a solution are given below in Table I.

Table I PROPERTIES OF ANHYDROUS NITRIC ACID-SPIRO ANDP-)ll]S:I;I IIl IQsQUATERNARY AMMONIUM COMPOUND MONOPRO- Unmixed Stoichiometric solutions with nitric acid Calculated compounds performance Compound 2 9 3} Storage Viscosity g of Oxidizer Freezing stability, Card Density, centistokes Molecular M. P., cmixture to fuel point 2 of hrs. to 100 gap gmJml. Igp O./F.3

weight O. weiqht ratio, solution, p.s.i.ut value, at C. max.

.2 Wa/Ws F. 200 F. cards 75 F. 32 F. F. peiccnt N,N-pentamethylenepiperidinium nitrate 216.3 180-190 24.1 3.15 -62 36 80-100 1. 40 3.8 247.9 2.60 N,N ,N,N-dietl1ylcnedipipcridiniurn d1' nitrate 348.4 355 27.6 2.98 -86 250 62- 75 1. 47 24.6 248.2 2. 40 N ,N,N,N-diethylenedipyrrolidinium dinitrate 320.3 296 dec. 29.8 2.36 -58 500 21-23 1.48 33.8 248.4 1. 97 (Cavea A) N,N-dimethyltriethylencdiammonium dinitrate 266.3 274-277 35.6 1.81 -43 M 912 10- 11 1.51 7.3 15 45 251.3 1.

1 Weight of acid/weight of salt.

2 Temperature at which crystal separation begins.

3 Oxidizer to fuel ratio.

4 Test stopped because of mechanical difiiculties.

A 470 at 250 F. which contained nitric acid (200 grams, 3.19 moles) and water (200 milliliters). The addition was made while a stream of air was bubbled through the stirred acid solution. After the addition was complete, which took about one hour, stirring was continued at 50 C. (122 F.) with air passing through until the solution was free of the bromine which was constantly evolved. The mixture was cooled and diluted with an equal volume of acetone and with a twofold volume of diethyl ether. The crystalline material which formed was filtered and recrystallized from 95 percent methanol. A near quantitative yield of the dinitrate salt was obtained which did not melt when heated to 355 C. (671 F.).

N,N',N,N'-DIETHYLENEDIPYRROLIDINIUM DINITRATE (a) N,N',N,N-diethylenedipyrrolidinium dibr0mz'de.-

A mixture of pyrrolidine (248.5 grams, 3.5 moles), sodium hydroxide (140 grams, 3.5 moles) and water (420 milliliters) was stirred and ethylene bromide (658 grams, 3.5 moles) was added dropwise at such a rate that the mixture refluxed (95 C., 203 F.). After the addition, the mixture was stirred and refluxed for 6 hours. The mixture was then cooled and the precipitated product was filtered and washed with methyl alcohol. The crystalline material was purified by dissolving it in water, adding Norite, boiling and filtering. To the filtrate was added twice its volume of isopropyl alcohol whereupon a very fine white material separated. The product was filtered,

washed with acetone and vacuum dried. It melted when heated to 341 C. (645 F.).

(b) N,N,N,N' diethylenedipyrrolidinium dinitraze.- N,N',N,N' diethylenedipyrrolidinium dibromide (130 The data given in the above Table I show that the thermal stability of the tested monopropellants of the invention ranges from 36 hours to more than 500 hours. The card gap tests show that the monopropellants are resistant to detonation by shock. Freezing points are all below -5 8 F., showing that the monopropellants are suitable for use under arctic or high altitude conditions. The viscosities show that the monopropellants can be readily pumped at temperatures at least as low as -40 F.

The data in the above Table I also show that said monopropellants of the invention are superior to the monopropellant prepared using the compound Cavea A with respect to (a) viscosity at 40 F., and (b) freezing point. Said Cavea A is a non-spiro quaternary ammonium compound generally considered to be superior with respect to its propellant properties when mixed with nitric acid. It is to be noted that said improvement in viscosity at -40 F. and in freezing point are obtained Without any appreciable sacrifice in I values.

As will be recognized by those skilled in the art, an improvement in one or more properties of a propellant, or a different combination of values, is very often a valuable contribution to the art.

The procedures used in carrying out the tests in the above example is outlined below.

The thermal stability tests were carried out at 200 F. on stoichiometric mixtures of the spiro or dispiro quaternary ammonium compounds in anhydrous nitric acid. The procedure followed can be summarized as follows. A small glass tube, constructed from fit-inch (I.D.) glass pipe which is able to withstand pressure greater than 1000 psi, is filled about two-thirds full (about 6 ml.) with the monopropellant to be tested. This tube is fit-ted with a safety head containing a rupture disk which will rupture at about 200 p.s.i. pressure. Said small glass tube or bomb is then placed in a constant temperature bath, containing cold water, and is connected to a pressure recorder and to a supply of compressed nitrogen gas. The pressure in said bomb is raised to 110 p.s.i. with nitrogen to check the system for leaks after which the pressure in said bomb is reduced to 20 p.s.i. The temperature in the constant temperature bath, which can be regulated to maintain a temperature of 200 F., is increased and the time at which a temperature of 200 F. is reached is taken as the start of the test. The test is terminated when the pressure in said bomb exceeds 100 p.s.i. or when the rupture disk is ruptured (the pressure rise is often rapid after 100 p.s.i. is reached). The storage life of the propellant at 200 F. is recorded as the time necessary for the pressure in said bomb to increase from 20 to 100 p.s.i.

The shock sensitivity of the monopropellants was determined by the American Rocket Societys Recommended Card Gap Test No. 1, Committee on Monopropellant Test Methods, July 12, 1955. Basically said test consists of placing a 40 ml. sample of the monopropellant above a 50 gram tetryl booster charge and determining the number of 0.01 inch thick cellulose acetate disks (cards) which must be inserted between said booster and the monopropellant to prevent detonation of said monopropel-lant sample.

The data for the card gap test are herein recorded as a range from the highest number of cards which do not prevent detonation to the lowest number of cards which prevented detonation. The shock stability is inversely related to the card gap range.

The viscosities were determined with a Fenske viscom eter following the procedure substantially as stated in ASTM test D445.

The densities were determined with a Westphal balance.

The approximate freezing points were determined by cooling the solution to the temperature at which crystal separation began. Some of the tests were terminated at temperatures above the freezing point in view of the low values.

It is to be realized that the storage stability test at 200 F. is a severe test and the mere fact that some compounds give mixtures which have a relatively low storage stability at 200 F. does not mean that said compounds are not useful in the practice of the invention because, at lower temperatures, mixtures of said compounds with nitric acid do have higher storage stabilities than those shown in Table I and can be used at lower temperatures in those instances where storage stability is of secondary importance.

The calculated performance (I values of the monopropellants of the invention were calculated using the following formula and assuming frozen combustion gas composition during isentropic expansion of combustion gases in the rocket nozzle.

c+ e am' 2 in m" In 212 T is the combustion temperature (or reaction temperature) in the rocket engine in degrees Rankin.

T is the temperature of the combustion gases after expansion at the nozzle exit (assuming isentropic, optimum expansion) in degrees Rankin.

P is the combustion chamber pressure in atmospheres.

F is the pressure in atmospheres at the nozzle exit.

R is the universal gas constant.

g is gravitational conversion factor.

lb. mass ft. 1b. force sec.

M is the average molecular weight of combustion gases at combustion chamber conditions.

Since many possible embodiments may be made of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. A monopropellant composition comprising a mixture of (1) an oxidant selected from the group consisting of nitric acid containing at least about 70 weight percent HNO and mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 weight percent HClO and not more than about 30 weight percent water, and (2) at least one compound selected from the group consisting of spiro quaternary ammonium compounds characterized by Formula I below and dispiro quaternary ammonium compounds characterized by Formula II below, and mixtures thereof,

11 i I i c I T E R x E; N X N H RHC CHE. x I

RHC GliR c Formula I R y a. lb

Formula II wherein: each R is selected from the group consisting of a hydrogen atom and alkyl radicals containing from 1 to 3 carbon atoms, and wherein not more than one R in each ring is an alkyl group; x and y are each integers of from 4 to 8; X is an anion selected from the group consisting of nitrate, perchlorate, monohydrogen phosphate, dihydrogen phosphate, hydrogen sulfate, sulfate, hydroxyl, orthoborate, dihydrogen borate, and tetraborate anions; a and b are each integers of from 1 to 4, and the product of a multiplied by the number of quaternary nitrogen atoms is equal to the product of b multiplied by the valence of said anion X; and wherein the ratio of said quaternary ammonium compound to said oxidant is with in the range of 0.75 to 1.25 times that of the stoichiometric amount.

2. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N,N',N'-di'(tetramethylene)piperazinium dinitrate.

3. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N-tetramethylene- N,N'-pentamethylenepiperazinium dinitrate.

4. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N,N',N'-di(pentamethylene)piperazinium dinitrate.

5. The monopropellant of claim 1 wherein said quaternary ammonium compound i N,N-tetramethylenepyrrolidinium nitrate.

6. The monopropellant of claim 1 wherein said qua- 11 ternary ammonium compound is N,N-(1-methyltetra methylene) -2-methylpyrrolidinium nitrate.

7. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N-pentarnethylenepiperidinium nitrate.

8. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N-(1-methylpentamethylene)-2-methylpiperidinium nitrate.

9. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N-pentamethylenepyrrolidinium nitrate.

10. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N-hexamethylenepyrrolidinium nitrate.

11. In the method for development of thrust by the combustion of a monopropellant in the combustion chamber of a reaction motor, the step comprising injecting into said combustion chamber a mixture of (1) an oxidant selected from the group consisting of nitric acid containing at least 70 weight percent HNO and mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 weight percent HClO and not more than about 30 weight percent water, and (2) at least one compound selected from the group consisting of spiro quaternary ammonium compounds characterized by Formula I below and dispiro quaternary ammonium compounds characterized by Formula 11 below, and mixtures thereof,

Formula II wherein: each R is selected from the group consisting of a hydrogen atom and alkyl radicals containing from 1 to 3 carbon atoms, and wherein not more than one R in each ring is an alkyl group; x and y are each integers of from 4 to 8; X is an anion selected from the group consisting of nitrate, perchlorate, monohydrogen phosphate, dihydrogen phosphate, hydrogen sulfate, sulfate, hydroxyl, orthoborate, dihydrogen borate, and tetraborate anions, a and b are each integers of from 1 to 4, and the product of a multiplied by the number of quaternary nitrogen atoms is equal to the product of b multiplied by the valence of said anion X; and wherein the ratio of said quaternary ammonium compound to said oxidant is within the range of 0.75 to 1.25 times that of the stoichiometric amount.

12. The method of claim 11 wherein said quaternary ammonium compound is N,N,N',N'-di(tetramethylene)- piperazinium dinitrate.

13. The method of claim 11 wherein said quaternary ammonium compound is N,N tetramethylene N',N'- pentamethylenepiperazinium dinitrate.

14. The method of claim 11 wherein said quaternary ammonium compound is N,N,N',N'-di(pentamethylene)- piperazinium dinitrate.

15. The method of claim 11 wherein said quaternary ammonium compound is N,N tetramethylenepyrrolidinium nitrate.

16. The method of claim 11 wherein said quaternary ammonium compound is N,N-(1-methyltetramethylene)- Z-methylpyrrolidinium nitrate.

'17. The method of claim 11 wherein said quaternary ammonium compound is N,N-pentamethylenepiperidinium nitrate.

18. The method of claim 11 wherein said quaternary ammonium compound is N,N-(1-rnethylpentamethylene)- Z-methylpiperidinium nitrate.

19. The method of claim 11 wherein said quaternary ammonium compound is N,N- pentamethylenepyrrolidinium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A MONOPROPELLANT COMPOSITION COMPRISING A MIXTURE OF (1) AN OXIDANT SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID CONTAINIG AT LEAST ABOUT 70 WEIGHT PERCENT HNO3 AND MIXTURES OF SAID NITRIC ACID WITH PERCHLORIC ACID WHEREIN SAID MIXTURES CONTAIN UP TO ABOUT 50 WEIGHT PERCENT HCIO4 AND NOT MORE THAN ABOUT 30 WEIGHT PERCENT WATER, AND (2) AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF SPIRO QUATERNARY AMMONIUM COMPOUNDS CHARACTERIZED BY FORMULA I BELOW THE DISPIROQUATERNARY AMMONIUM COMPOUNDS CHARACTERIZED BY FORMULA II BELOW, AND MIXTURES THEREOF, 